1. Field of the Invention
The present invention relates to a liquid droplet ejection apparatus, and more particularly, to a liquid droplet ejection apparatus which forms images on a recording medium by ejecting ink droplets onto the recording medium.
2. Description of the Related Art
An inkjet type liquid droplet ejection apparatus forms images on a recording medium by ejecting ink droplets from a plurality of nozzles (apertures) toward a recording medium, such as paper, while moving the recording medium and an ink ejection head having an arrangement of the nozzles relatively with respect to each other.
In recent years, improvements in image quality have been sought by increasing nozzle density, and hence the amount of ink ejection onto the recording medium has been increasing. Generally, the ink used in a liquid droplet ejection apparatus of this kind has a large content of liquid solvent, such as water, organic solvent, or the like.
If the recording medium is a permeable medium in which the ink permeates into the interior of the medium, so-called “bleeding” arises as the ink permeates into the recording medium, in that the dot size becomes larger than the intended diameter, the boundary regions of the dots become blurred, the spreading of the dots becomes uneven, or the dots form a bearded shape.
Furthermore, even if the recording medium is a non-permeable medium in which the ink becomes fixed principally on the surface of the medium, then if the solvent component in the ink applied to the recording medium is not removed sufficiently, it is not possible to stably fix the coloring material component in the ink on the surface of the recording medium.
Therefore, treatment liquid droplets which cause to the coloring material in the ink droplets to become insoluble or to aggregate, are ejected toward the recording medium, whereupon, ink is ejected and the coloring material is thus caused to aggregate on the recording medium. In particular, if the recording medium is a permeable medium, then the coloring material is made to collect on the surface of the medium, and only the solvent component is made to permeate into the medium. Furthermore, if the recording medium is a non-permeable medium, the coloring material and the solvent are made to separate and only the solvent component is removed. Various liquid droplet ejection apparatuses capable of improving the image quality by adopting compositions of this kind have been proposed.
Japanese Patent Application Publication No. 08-052867 (in particular, FIGS. 4 to 7 and paragraphs 0027 to 0033) discloses an apparatus in which control is implemented in such a manner that treatment liquid dots are formed at the ink dot formation positions, in accordance with the distribution of the ink dots, whereas no treatment liquid dots are formed at positions where no ink dots are to be formed, and furthermore, by making the ejection volume of one droplet of treatment liquid greater than the ejection volume of one droplet of ink, and hence forming the treatment liquid dots to a larger size than the ink dots, one dot of treatment liquid is formed so as to cover the formation region of a plurality of ink dots on the recording medium.
Japanese Patent Application Publication No. 11-334114 (in particular, FIGS. 2 to 7 and paragraphs 0022 to 0031) discloses an apparatus in which quantized data for ink, which are quantized into n values (for example, 5 values) at a prescribed resolution, are determined in accordance with image data, and by assigning ink dots and treatment liquid dots respectively to matrices each comprising a plurality of pixels (for examples, matrices of 2×2 pixels), in accordance with the quantized ink data, the formation positions of the recording liquid dots are controlled in accordance with the state of distribution of the ink dots.
Japanese Patent Application Publication No. 2002-337332 discloses an apparatus which forms high-quality images by depositing droplets in three superimposed layers in the order of: ink, treatment liquid, and ink; or treatment liquid, ink, and treatment liquid.
If droplets of treatment liquid are ejected onto a recording medium, and ink droplets of a first color (for example, magenta), and then ink droplets of a second color (for example, cyan) are ejected in sequence onto the positions on the recording medium where the treatment liquid droplets have been deposited, then the ink droplets of the first color ejected immediately after the treatment liquid droplets make direct contact with the fresh treatment liquid droplets on the recording medium and react satisfactorily with same, whereas the ink droplets of the second color that are ejected subsequently do not make direct contact with the fresh treatment liquid droplets, and in general, the ink droplets of the second color react to a lesser extent than the ink droplets of the first color. In other words, the treatment liquid does not act uniformly on the ink droplets of the first color and the ink droplets of the second color.
Furthermore, if the number of ejection cycles of the treatment liquid is increased in order that the treatment liquid acts uniformly on the ink droplets of the first color and the ink droplets of the second color, in such a manner that droplets are ejected in the order: treatment liquid droplet, first color ink droplet, treatment liquid droplet, and second color ink droplet, onto the same positions on the recording medium, then the amount of treatment liquid deposited on the recording medium increases.
Even if a composition is adopted in which treatment liquid dots are formed at ink dot formation positions and treatment liquid dots are not formed at position where ink dots are not to be formed, on the basis of the state of distribution of the ink dots, as described in Japanese Patent Application Publication No. 08-052867, then in cases where an. image is to be formed over the whole surface of a broad recording medium, ultimately, a large amount of treatment liquid is deposited on the recording medium. For example, if a large photographic image is to be formed on a recording medium, then ultimately, a large amount of treatment liquid is deposited on the recording medium, in any case.
Moreover, even if the treatment liquid dot formation positions are controlled on the basis of quantized ink data, as described in Japanese Patent Application Publication No. 11-334114, in cases where the level of the quantized data corresponding to the amount of treatment liquid to be deposited per unit surface area (for example, a matrix of 2×2 pixels) is high, then ultimately, a large amount of treatment liquid is deposited. If inks of a plurality of colors are used, then in general, a very large amount of treatment liquid is deposited when an image is formed over the whole surface of the medium at a neutral color tone.
Furthermore, none of Japanese Patent Application Publication Nos. 08-052867, 11-334114 and 2002-337332, describes causing the treatment liquid to act uniformly on ink droplets of a first color and ink droplets of a second color.